Along an assembly line, diapers and various types of other disposable absorbent articles may be assembled by adding components to and otherwise modifying advancing, continuous webs of material. Webs of material and component parts used to manufacture diapers may include: backsheets, topsheets, absorbent cores, front and/or back ears, fastener components, and various types of elastic webs and components such as leg elastics, barrier leg cuff elastics, and waist elastics. In some configurations, graphics are printed on individual components and/or continuous webs of material used to assemble the absorbent articles. The graphics may be provided by printing ink on substrate materials by various printing methods, such as flexographic printing, rotogravure printing, screen-printing, inkjet printing, and the like.
In some configurations, printing operations are performed separate to the assembly process, such as for example, printing the substrates offline wherein the printed substrates may be stored until needed for production. For example, printing operations may be accomplished on discrete printing lines, separately from converting lines that are dedicated to manufacturing disposable absorbent articles. After printing on the printing lines, the printed substrates are delivered to the converting lines, such as in a form of continuous webs comprising printed images thereon. In addition to or alternatively to offline printing, graphic printing may be done online during the article assembly process.
Some current printing operations may utilize solvent and/or aqueous based inks to print graphics. However, solvent and/or aqueous based inks may require additional processing steps after the ink is printed. Such additional process steps may include drying operations that may require evaporation of some ingredient of the inks, such as a solvent or a thinner. External heating systems may also be required to complete these drying steps. As such, the required drying steps may be difficult to complete at relatively high manufacturing and/or printing speeds to ensure printed inks are adequately dried before subjecting printed substrates to additional processing operations. In order to avoid the drying steps that may be required when printing with solvent and/or aqueous based inks, some printing operations may utilize wax based inks that may have a solid state at room temperature. Before printing, the wax based inks may be heated and converted to a liquid state. The wax based inks may then be printed onto a substrate while in the liquid state. The printed wax based ink then solidifies when cooled. However, wax based inks may require specific types of printing devices that are particularly configured to print liquids having the properties of wax based inks. Additional heating and fluid handling systems may be required to ensure the wax based inks are maintained in a liquid state before being applied to a substrate. In addition, it may be difficult to adequately cool the ink at relatively high manufacturing and/or printing speeds to ensure printed inks are adequately solidified before subjecting printed substrates to additional processing operations.
In an attempt to overcome the aforementioned drawbacks related to printing with wax based inks and/or other inks that require drying operations, some printing operations may utilize energy curable inks that are cured by chemical reactions. Examples of energy curable inks may include ultraviolet curable inks. Unlike inks that need to be dried, once the energy curable ink is deposited in a liquid state on a substrate, the ink may be cured and solidified by subjecting the ink to a radiation source, such as ultraviolet light.
However, printing substrates with energy curable inks is not without challenges. For example, when printing on fibrous substrates, such as nonwovens, the printed ink may penetrate into the substrate. In some instances, the printed ink may flow or migrate entirely through the substrate from one surface to an opposing surface. In turn, radiation, such as ultraviolet light, directed toward one surface of a substrate intended to cure the printed ink may not reach ink that has migrated or flowed to an opposing surface and/or may otherwise be shielded from the ultraviolet light by fibers within the substrate. As such, some uncured ink may remain on the substrate after advancing past the radiation source. Such uncured ink may subsequently rub-off and/or otherwise migrate from the printed substrate to other components during product assembly or product use.
Consequently, there remains a need to configure energy curable printing systems to help ensure that ink that may flow through a substrate and/or otherwise may be shielded from a radiation source by fibers within the substrate is cured.